1. Field of the Invention
The present invention pertains to bone graft materials and, more particularly, to resorbable bone graft materials optimized for strength, injection and osteoconductivity and to methods of strengthening bones using injectable, resorbable bone graft materials.
2. Brief Discussion of the Related Art
Minimally invasive surgical procedures have become very popular in the orthopedic field; and accordingly, it has become desirable to be able to inject bone graft materials in a minimally invasive manner, such as via a syringe. Since it is desirable for some bone graft materials set or cure in the body, time constraints are an issue in that the bone graft materials must maintain sufficiently low viscosity to allow injection without requiring substantial ejection force but, after injection, should, desirably, cure quickly to provide compression strength as soon as possible. Additionally, it is preferred that bone graft materials be resorbable (bioabsorbable), as opposed to bone cement which is not, and osteoconductive. The MIIG® 115 injectable bone graft material, described in U.S. Published Patent Application 2003/0185903 and marketed by Wright Medical Technology, Inc., the assignee of the present invention, is an effective injectable resorbable bone graft material made from calcium sulfate hemihydrate; however, improvements are desirable relating to working time (the time period available in which the bone graft material can be implanted in the body), injectability (the relative force required to easily inject the bone graft material through associated instrumentation using hand and/or thumb force), the set or cure time relative to compressive strength, the compressive strength achieved one hour after injection and the compressive strength achieved 24 hours after injection. Calcium sulfate hemihydrate for use as bone graft materials have, in the past, been made using hydrothermal processes where calcium sulfate dihydrate is boiled in a reaction vessel under greater than atmospheric pressure and result in a structure which requires an undesirable amount of water for hydration.